Makefile.am: include common eu.am definitions

Makefile.am: include common eu.am definitions

Some definitions in Makefile.am can be moved
to the common definitions in config/eu.am,
but for them to apply to the top-level Makefile after moving,
eu.am must be added as an include statement.

Except for "CLEANFILES", handled in the next commit,
there are no definitions in eu.am that are defined in Makefile.am,
so there are no other conflicts or overrides between the two.

Signed-off-by: Michael Pratt <mcpratt@pm.me>